A machine translation device translates an original sentence written in a source language into a translated sentence written in a target language, and includes an input device for inputting the original sentence; original sentence analysis device for dividing the original sentence into single words and for analyzing syntactic structure of the original sentence; a translation dictionary for storing related words of a same meaning in at least three languages including the source language and the target language; dictionary reference means for referencing the translation dictionary and, when it finds an appropriate word in the target language corresponding to a word in the original sentence, for retrieving the word in the target language, while when there is no appropriate word in the target language, for retrieving a word in a predetermined language aside from the source language which corresponds to a word in the original sentence from the translation dictionary as an untranslated word; and translated sentence generation means for converting every word in the syntactic structure of the original sentence into words in the target language and untranslated words and, by using the syntactic structure in which every word has been converted, for generating the translated sentence.